In the foundry industry, one of the processes used for making metal parts is sand casting. In sand casting, disposable foundry shapes (usually characterized as molds and cores) are made by shaping and curing a foundry mix which is a mixture of sand and an organic or inorganic binder. The binder is used to strengthen the molds and cores.
One of the processes used in sand casting for making molds and cores is the no-bake process. In this process, a foundry aggregate, binder, and liquid curing catalyst are mixed and compacted to produce a cured mold or core. In the no-bake process, it is important to formulate a foundry mix which will provide sufficient worktime to allow shaping. Worktime is the time between when mixing begins and when the mixture can no longer be effectively shaped to fill a mold or core.
A binder commonly used in the no-bake process is a polyurethane binder derived by curing a polyurethane-forming binder with a liquid tertiary amine catalyst. Such polyurethane-forming binders used in the no-bake process, have proven satisfactory for casting such metals as iron or steel which are normally cast at temperatures exceeding about 1400.degree. C. They are also useful in the casting of light-weight metals, such as aluminum, which have melting points of less than 700.degree. C.
The polyurethane-forming binder usually consists of a phenolic resin component and polyisocyanate component which are mixed with sand prior to compacting and curing. The phenolic resin component generally contain small amounts of free phenol, free formaldehyde and organic solvent, all of which can be obnoxious to smell and can create stress for the environment. Because of this, there is an interest in developing foundry binders which do not contain free phenol, free formaldehyde, and organic solvents.